The present invention relates to an apparatus for forming images comprising an electrostatic charge retentive member arranged rotatably, means for forming an electrostatic latent image on the charge retentive member, means for developing the latent image with a toner to form a toner image, means for transferring the toner image onto a record paper and means for removing a residual toner on the charge retentive member.
There has been developed an electrophotographic copying machine in which a charge latent image corresponding to a document image is formed on a rotatable photosensitive drum, the latent image is developed with a two component dry developer including toner and magnetic carrier to form a toner image and then the toner image is transferred onto a record paper to form a duplicated copy. In such a copying machine, after the toner image has been transferred onto the record paper, but prior to forming a new latent image for a next duplication, it is necessary to clean the photosensitive drum to remove residual toner on the drum. Heretofore, there have been proposed various kinds of cleaning devices for removing the residual toner such as a fur brush cleaning device, a blade cleaning device and a magnetic brush cleaning device. In the copying machine in which the latent image is developed with the two component dry developer, it is preferable to collect the residual toner on the drum for the recovery. In the fur brush cleaning device, since the residual toner is brushed off the drum and is collected by a filter with the aid of an air flow passing through the filter, the residual toner collected by the filter could not be used again. Further, the fur brush cleaning device is liable to be large in size and complicated in construction, because it requires large and complicated air sucking mechanism and filter. Therefore, the copying machine having such a fur brush cleaning device is also liable to be large in size. Contrary to this, in the blade cleaning device, since a blade made of elastic material such as urethane resin is brought into contact with the photosensitive drum to scrape the residual toner off the drum, the construction can be made rather small and simple. Further, the scraped residual toner can be collected for the recovery. For this purpose, the residual toner scraped off the drum by the blade is once collected in a toner receptacle and then the collected toner is transferred into the developing device by a manual operation or is automatically transported into the developing device by means of a toner transporting means having a special construction such as a flexible screw. However, in the former case, the maintenance becomes cumbersome, because the toner is difficult to handle, and in the latter case, the toner transporting means becomes complicated.
In copying machines having the magnetic brush developing device, the developing device can be commonly used as the magnetic brush cleaning device and the cleaned residual toner is automatically collected in the developing device. Therefore, it is not necessary to effect the special maintenance and to arrange the complicated device for the recovery. In this type of copying machine, the developing device is arranged between a latent image forming station and a transfer station and thus the cleaning and developing operations could not be caried out simultaneously. Therefore, even in case of forming successively a plurality of copies for a document, the photosensitive drum must be rotated by at least two revolutions for each copy and a circumferential length of the drum must be made longer than a length of a record paper. This results in that the copying speed becomes low and the copying machine becomes large in size.
In a U.S. Pat. No. 3,552,850, there has been further proposed a blade cleaning device in which the residual toner collected by a blade can be transported into a cascade developing device without providing any transporting device having a special construction. In this known cleaning device, the blade is arranged movably between two positions, in one position the blade is brought into contact with the photosensitive drum and in the other position the blade is separated from the drum. When the blade is separated from the drum, an accumulation or a mass of the collected residual toner is released from the blade and passes underneath the blade, and then the toner accumulation on the drum is transported to the developing device due to the rotation of the drum. In the above mentioned U.S. Pat. No. 3,552,850, there is further disclosed another embodiment in which the blade is always urged against the drum and two grooves are formed in the drum surface. Then the residual toner accumulated by the blade is collected by the grooves and is transported into the cascade developing device, while the drum continues to rotate.
The blade cleaning device disclosed in the U.S. Pat. No. 3,552,850 may be applied to the copying machine comprising the magnetic brush developing device using the two component dry developer. In this case, the residual toner scraped by the blade and transported to the developing device due to the rotation of the drum is collected into the developing device by means of a magnetic brush.
In the known blade cleaning device described in the U.S. Pat. No. 3,552,850, the timing at which the cleaning blade is separated from the drum and thus the timing at which the toner accumulation passes underneath the blade are fixedly determined. Therefore, in case of forming continuously a plurality of copies for a document, the drum must rotate at least one revolution, even if the length of the record paper is shorter than the circumferential length of the drum, because otherwise the toner accumulation might situate within a charge latent image and thus a duplicated copy might be deteriorated to a great extent. Nowadays, there have been developed various copying machines which can use various kinds of record papers having different lengths. In such copying machines, when a continuous duplication is effected by using short record papers, a period during which a single copy is formed can be shortened as compared with a period during which a single copy of a longer record paper is formed. In the above mentioned known blade cleaning device, since the timing at which the cleaning blade is separated from the drum is fixed, it could not be applied to the copying machines in which the duplicating period can be varied in accordance with the lengths of record papers to be used.